Temperature-responsive magnetic material



March 19, 1929. KlNNARD 1,706,172

TEMPERATURE RESPONSIVE MAGNETIC MATERIAL Filed Nov. 11, 1925 Invemor:

15666. F. Ki nnard,

Hi sArromey t... Man 19,1929 UNITED STATES.

PATENT. OFFICE.

ISAAC I. KINNABD, OF LYNN, MASSACHUSETTS, ASSIGNOR '1'0 GENERAL ELECTRIC('iOMIE'AlhTY, A CORPORATION 0] NEW YORK.

'IEMFEBATUBE-BESPONSIVE GHETTO IATEBIAL.

Application filed l qovember 11, 1925. serial- No. 88,402.

My invention relates to magnetic material and in particular to magneticalloys having a substantiall linear negative temperature coefiicient 0permeability between ordinary temperature limits. Such a material isuseful in the construction of temperature responsive magnetic. devicesand.

for usein various electromagnetic devices to correct for temperatureerrors as described, for example, in my co ending apled May 5, 1924,assigned to the same assignee as the present invention, of which thepresent application is in part a continuation.

The-features, of my invention which-are believed to be novel andpatentable --will be pointed outin the claims appended hereto.

invention the alloys in question, properties W111 now be For a betterunderstanding 0 the method of making their composition an explained andreference will be made to-the accompanying drawing which shows in Fig.

1 temperature-permeability curves ofmaterial' pre aredin accordancewithmy invention. 1g. 2 1s a curve showing how the transformationpoint-of the material varies with the copper content; and Figs. 3 and 3give the results of hysteresis tests on the material.

' I have discovered that certain coppernickel alloys when roperlyprepared can be made to have, in a dition to other desirable properties,a substantially linear negative temperature coefiicient of permeabilitybetween ordinary temperature limits. and that this characteristic may becontrolled and varied by varying the composition of the alloy and themethod of preparation.

Most magnetic material has more or less hysteresis loss. That is to say,the magnetism of the material lags behind the force producing themagnetism such that the magnetism. for a given producing force will beless if the force is increasing than it would be if the force weredecreasing. This property gives rise to the well known hysteresis loopcharacteristic of magnetic materials. It will be readily expected that amaterial having. a negative temperature coeflicient of permeability andhaving appreciable hysteresis loss would have different values ofmagnetism at a given temperature when crease or an increase intemperature. However, if such material had a very low or inappreciablehysteresis loss, it would be expected that it would always have the samemagnetism under the above conditions irrespect ve of the direction ofchange in temperature. My investigations have shown the above theory tohol good. In order to utilize the negative temperature coeflicient ofpermeabilit characteristic ofa magnetic material to t e bestv advantageit. is of course desirable that the rmeability vary with the temperaturean be independent of the direction oftemperature chan e as otherwisethematerialwould give di erent results at a given temperature,'dependingupon whether the temperature was increasing or decreasing. It istherefore desirable that such material have-zero or negli iblehysteresis and it is one-of the objects 0 my invention to provideamaterialhaving these desirable properties.

adding ,sufiicient additional iron to bring the total percentage up tothe value desired. It is possible to obtaindesirable results at a lowcost in this manner. An alloy containing approximately the percentagesof copper, nickel and iron above specified when prepared as describedhereinafter gives a permeability temperature curve as shown in curve Aof Fig. 1. It will be noted that the curve is a proximately straightbetween 0 and 100 and below about C. corresponding to range oftemperatures where the material will be ordinarly used, the curveissubstantiall straight. Another desirable feature of this material, asmay be seen from the curve, is that it approaches unity permeabilityvery gradually. The percenta e of copper used also varies the point oftransformation. Thus curve of Fig. 2 shows how the point of transforma-I, have found that the effect of adding a small amount of iron tocertain copper tion varies with changes in the per cent of copper, theiron content being maintained constant at about 2.2 per cent and thenickel content varying inversely as the copper. 5 Curve B of Fig. 1shows the characteristics of an alloy containing approximately 60 ercent nickel and 40 per cent copper. In t is case the permeabilitybecomes negligible at about 14 C.

The heat treatment given during the preparation of the alloys is veryimportant if the desired characteristics and uniformity of product areto be obtained. To obtain an alloy having the characteristics given in 1curve A of Fig. 1, I prefer to use the following method: The followingingredients are melted in an Ajax high frequency induction furnace:

7 Per cent. 11100 X nickel shot 68.2

Clean copper scrap (pure) 30.

A chemical analysis of the Inco X nickel shot shows the composition tobe as follows:

Commercially pure iron pure, the t eoretical composition of the alloy isas follows:

Per cent. Nickel 67.25 Copper 30.12 Iron 2.4

Impurities 0.23

A typical chemical analysis of the finished alloy is as follows:

Per cent.

Nickel 67.35 Copper 30.17 Iron 2.08

Impurities Some of the iron is evidently lost through oxidation. Theimpurities apparently have no influence on the temperature permeabilitycharacteristics.

The alloy is' heated to approximately 1650 C. before pouring. Noadditional stirring is necessary as the electromagnetic forces acting onthe molten metal in this type of furnace produce a stirring actionsufiicient to thoroughly mix the alloy. Preferably, immediately beforepouring, 0.15% of magnesium wire is added to the melt in order. todeoxidize the alloy. This deoxidation apparently has littleor no effecton the magnetic roperties of the material, but it has the e ect ofmaking the al low malleable, while without deoxidation it would bebrittle.

The alloy is cast in green sand molds and as soon as the castings havesolidified, they are seized with tongs and plunged into cool water.

A test piece of standard size weighing about 5 grams is cut from one ofthe castings from a temperature lower than the original quenchlngtemperature.

Material having a releasetemperature higher than 105 C. may have itsrelease point lowered by heating to 1050-1100 C. and quenching in oil.

The same general rocedure is followed in making other alloys avingdifferent release points, the characteristics being varied as desired byvarying the percentage composi tion of iron, copper and nickel aspreviously pointed out. When thus prepared the materials are malleableand have a negligible hysteresis loss and ver low retentivity. Thecurves of Fi, 3 give the results of hysteresis test of an alloy havingthe properties shown in curve A, Fig. 1. It will be noted that thehysteresis loss is so small that it can be hardly detected on thiscurve. The lower part of the curve is enlar ed in Fig. 3. This mate rialhas a specific resistance of about 49 microns per centimeter cube.Another unusual characteristic is its low retentivity which is onlyabout 8 per cent of the maximum induction.

The importance of uniform temperature treatment to obtain a uniformproduct cannot be overelnphasized. For example I have found that thealloy which gives the characteristics of curve A, Fig. 1, when preparedas previously described is very sensitive to heat treatment both beforeand after solidifying in the mold. If this same material is poured in agraphite mold instead of a sand mold, the resulting material ispractically non-magnetic at 20 C. If poured in a mold of zirconiumsilicate, it becomes substantially non-magnetic at 60 C. If this lastmentioned sample is then heated for two hours at 700 .C. and cooled inair, its release point is raised to 98 C.

It will be seen therefore that in order to obtain uniformity in resultsit is necessary to very carefully control the conditions un derwhich-the alloys are made as well as the percentage composition of thealloy. I believe the linear temperature-permeability relationship ofthese materials is due to the non-homo eneous manner in which the copperis hel in solution, which givestlie ef fect of the summation of a largenumber of alloys, each having a different transformation point. Theydiffer from Monel metal in this respect. Monel metal is a natural alloyof copper and nickel which has a negative temperature coefiicient ofpermeability over a short range of temperature, but which does not havethe desirable straight line characteristics shown in Fig. land is notsuitable for many purposes because its permeability drops very abruptlyas it approaches zero.

It is believed that the, desirable magnetic ,characteristics of thealloys which I have described and the manner in which the characmethodof preparation but seek claims cominensurate with the true spirit andscope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. An alloy containing between 60 and 80 per cent nickel and between and20 per cent copper and having substantiall a linear negative temperaturecoefficient o permeability which gradually becomes less'as thepermeability of the material approaches that of air at some temperaturebetween .10 and 110 0.

2. A malleable, magnetic'alloy containing between 60 and 80 per centnickel and between 40' and 20 per cent copper having a negligiblehysteresis loss and having a substantial negative temperatureveo'efiicient of permeability which gradually becomes less as thepermeability of the alloy'approaches that of air.

3. A magnetic alloy containing between and.80 per cent nickel, between40 and 20 per cent copper, and approximately 2 per cent iron having asubstantial and approximately a linear negative temperature coefiicientof permeability between 0 and 100 C. and having a permeability whichapproximibtesC that of air in the neighborhood of 10 9 4. A malleablemagnetic material contain-- gible hysteresis loss and having asubstantialand approximately a linear negative temperature eoefiicientof permeability between unity in the neighborhood of 100 C.

5. A heat treated east magnetic'alloy having a predetermined negativetem erature coefficient of permeability formed A .7 mixing approximately68 parts of hit el, 30 parts of copper, and 2 parts of iron in themolten state, casting said alloy in-a sandmold and quenching in water assoon as the alloy solidifies.

6. A magnetic material having a temperature crmeability characteristicwhich ap proac ies unity at about 100 C. and which Increasessubstantially uniformly with de-- crease in teinperature below about 100C. over a wide range-of temperature, consisting 0 and 100 C. whichgradually reduces to of a copper-nickel alloy containing between 40 and20 per cent copper, between (SO'aiid per cent nickel, and a smallamountiolf iron.

7. A cast material containing between 20 and 40 percent copper andbetween 60 and 80 percent nickel which is quenched from a temperaturesli htly below that at which the material solidi es and in which thepermeability ofthe material approaches unity at I some temperature pointabove 15 C. and in-v creases substantially uniformly with a de creas'eintemperature from such po nt down-' gvbam over a temperature range of atleast 8. A magnetic copper-nickel alloy containing between 60 and 80 percent nickel and between 40 and 20 a negligible hysteresis loss andhaving a substantia and approximately linear negative temperaturecoefiicient of permeability over a temperature range in excess of 40centigrade degrees.

.9. A magnetic copper-nickel alloy having a negligible hysteresis lossand having a substantial and approximately linear negative temperaturecoefiicient of permeability over a wide temperature range, the coppercontent of said alloy being between 20 and 40 er cent and being held insolution in a nonomogeneous manner.

:10. A magnetic copper-nickel alloy containing a small percentage ofiron having a negligible hysteresis loss and having a substantial'and aproximately linear negative temperature coe a wide tem erature range, thecopper content of said alloy being between 20 and 40 cient ofpermeability over per cent copper, having er cent and being held insolution in a nonomogeneous manner.

In witness whereof, I have hereunto set my hand this ninth day ofNovember, 1925.

ISAAC F. KIN NARI).

